This invention relates to an improved switching valve for dispensing fluids to a pumping outlet and, more particularly, to a more sensitive, efficient valve for selectively switching between fluid sources in response to a vacuum created at one of the sources.
It is well known to use switching or change-over valves having valve elements which are movable in response to a pressure differential in one of its inlets. The valve elements generally assume one of two positions corresponding to the flow through condition where one of the inlets is connected with the outlet. Such valves are used in a variety of applications ranging from the handling of oxygen and gases in medical, industrial and aerospace areas to liquid compositions, syrups and inks in the food and beverage handling and chemical industries. Depending on the application, the switching valve may include linearly movable spools, diaphragms and springs cooperable to provide the desired degree of responsiveness or sensitivity.
For example, in U.S. Pat. No. 2,651,491, to Ashton, et al. a shuttle valve is disclosed which utilizes a movable valve spool held in position by a centrally located detent mechanism. However, the unilateral design of the detent mechanism can cause the valve spool to be unstable, resulting in jamming and wear to the valve parts. U.S. Pat. No. 3,533,431 to Kuenzel appeared to improve on the problem of instability in previous valves by employing a cylindrical valve holding and release member to provide a better snap-acting switching valve. However, this arrangement is susceptible to wear of its valve elements, in the form of O rings and lacks pressure responsiveness for certain applications. Likewise, in U.S. Pat. No. 3,008,481, Matheson's differential pressure selector is susceptable to O ring wear and must rely on continuous pressure and precision molded parts to provide reliable switching and sensitivity.
More recent developments to switching valves have focused on responsiveness through the use of bistable spring arrangements such as shown in Du U.S. Pat. No. 4,467,941 and Hartley U.S. Pat. No. 4,493,435. Du '941 discloses a diverter valve having a valve member which is biased by an over center latching spring/diaphragm assembly. This provides a snap action, sensitive valve but is vulnerable to the same O ring wear problems experienced in prior art valves and appears to require special care in maintenance and reassembly. Hartley '435 shows a selector employing a bistable leaf spring drivingly coupled to a valve element with lost motion and cooperating with a multimember actuator assembly. While this device produces automatic, snap type switching, it is a complex arrangement seemingly difficult to repair and costly to manufacture.
Thus, various attempts have been made in the prior art to upgrade sensitivity, responsiveness, and durability in switching valves by provision of different actuators, seating and sealing elements and holding arrangements. However, there remains a need in this well developed art for a versatile, switching valve which is capable of efficient switching of fluids in the presence of a pressure differential in one of the inlets of the valve without the inherent drawbacks of the prior art. For instance, in some prior devices, the mechanisms used to establish the operating positions of the valve are unbalanced and can cause the movable spools to deviate from their axially oriented direction of travel and eventually stick or bind as high frictional forces are created. This misalignment can then cause wear or loss of sealing elements and resultant leakage. In other cases, the actuator used to sense the pressure differential and move the spool or valve element produces flow interruption or timing problems. These are particularly sensitive concerns when switching valves are used in the handling of fluids having different viscosities.
Accordingly, it is a principal object of the invention to provide an improved switching valve for alternatively and automatically or manually switching fluid sources to an outlet upon detection of a pressure differential caused by one of the sources.
Another object of the inventions is the provision of a switching device having improved sensitivity and responsiveness to changes in pressure.
Another object of the invention is to provide a simple, compact switching valve with a small number of parts which is reliable in operation and easy to manufacture and maintain.
Another object of the invention is to furnish a switching valve which minimizes frictional forces, misalignment, worn parts and leakage.
A still further object of the invention is to provide a switching valve which is capable of handling a variety of fluids without sacrificing efficiency.
One of the salient features of my invention is an improved actuating and detent arrangement for the switching valve.
An attendant feature of my invention is found in the particular sealing valves used in the switching valve.
A further feature of my invention is the balanced operation of the spool in the switching valve.
Another feature of my invention is found in the snap action operation provided by the cooperation of dual spring arrangements.